Kana Nemoto

Detection of small particles in fluid flow using a self-mixing laser

We describe a highly sensitive, real-time method of detecting small particles in a fluid flow by self-mixing laser Doppler measurement with a laser-diode-pumped, thin-slice solid-state laser with extremely high optical sensitivity. Asymmetric power spectra of the laser output modulated by the re-injected scattered light from the small particles moving in a dilute sample-flow, through a small-diameter glass pipe, were observed. The observed power spectra are shown to reflect the velocity distribution of the fluid flow, which obeys Poiseuille’s law. Quick measurements of flow rate and kinetic viscosities of water-glycerol mixtures were also performed successfully. Measurable low-concentration limits for 262-nm polystyrene latex spheres and 3-μm red blood cells in a fluid flow were below 1 and 10 ppm, respectively, in the present self-mixing laser Doppler velocimeter system.

Polarization properties of laser-diode-pumped microchip Nd:YAG ceramic lasers

Detailed oscillation spectra and polarization properties of laser-diode-pumped ceramic Nd:YAG lasers were examined. Inherent segregation of lasing patterns into local modes possessing different polarization states and oscillation frequencies was observed. Single-frequency, linearly polarized stable oscillations were achieved by forcing the laser into Ince-Gaussian mode operation by adjusting azimuthal cavity symmetry.

Microanalysis of Brownian Particles and Real-Time Nanometer Vibrometry with a Laser-Diode-Pumped Self-Mixing Thin-Slice Solid-State Laser

Doppler particle sizing by self-mixing laser was demonstrated by using a laser-diode-pumped thin-slice Nd:GdVO4 laser with extreme optical sensitivity. A substantial improvement of optical frequency shifters led to quick and accurate sizing of Brownian particles with concentration as low as 50 parts per billion (ppb) for 262-nm polystyren latex spheres in water. A successful real-time measurement of sub-nanometer vibrations was also demonstrated with the present self-mixing laser.

Linearly Polarized Single-Frequency Oscillations of Laser-Diode-Pumped Microchip Ceramic Nd:YAG Lasers with Forced Ince–Gaussian Mode Operations

Detailed oscillation spectra and polarization properties have been examined in laser-diode-pumped (LD-pumped) microchip ceramic (i.e., polycrystalline) Nd:YAG lasers and the inherent segregation of lasing patterns into local modes possessing different polarization states was observed. Single-frequency linearly-polarized stable oscillations were realized by forcing the laser to Ince–Gaussian mode operations by adjusting azimuthal cavity symmetry.

Simple Real Time Trace Nitrogen Dioxide Detector Based on Continuous-Wave Cavity Ringdown Spectroscopy Using Passively Locked External Cavity Diode Laser

We report on a compact trace nitrogen dioxide (NO2) detector based on cavity ringdown spectroscopy (CRDS), using a passively locked external cavity diode laser (PLEC-DL) in the visible wavelength region. Tailoring the spatial mode matching conditions of an antireflection (AR)-coated diode laser with a high finesse external cavity for effective optical feedback into the DL allows for stable resonant enhancement in the external cavity without any electric feedback apparatus. The external cavity having a finesse in excess of 1.4×105 acts as a ringdown cavity with an effective optical volume (i.e., detection volume) of less than 1 cm3. We successfully demonstrated a noise equivalent absorption loss of 1.4×10-8 cm-1, corresponding to a detection limit of 40 ppb NO2 concentration with a very compact configuration. For differential absorption CRDS, we realized a dual wavelength-locked PLEC-DL in an external cavity simultaneously. Measurements of various NO2 concentrations in N2 based on differential absorption CRDS were performed.

Detection of small particles in fluid flow with a self-mixing laser

Highly sensitive, real-time detection of small particles in fluid flow has been demonstrated by using a laser-diode-pumped, self-mixing thin-slice Nd:GdVO4 laser. Power spectra of modulated laser output, reflecting the velocity distribution of liquid flow, due to the scattered light from small particles in fluid flow were observed.

Experimental observations of dual-polarization oscillations in laser-diode-pumped wide-aperture thin-slice Nd:GdVO 4 lasers

Dual-polarization oscillations (DPO) on different transitions have been observed for the first time in a mirror-coated thin-slice Nd:GdVO(4) laser possessing a large fluorescence anisotropy with laser-diode (LD) pumping. Oscillation spectra, input-output characteristics, pump-dependent pattern formations and noise power spectra are studied experimentally. Simultaneous oscillations of orthogonally-polarized different (higher-order) transverse modes and the resultant violation of inherent antiphase dynamics in multimode lasers have been demonstrated. The experimental results have been explained in terms of the reduced three-dimensional cross-saturation of population inversions among orthogonally-polarized modes peculiar to LD-pumped wide-aperture anisotropic lasers, in which a pumped area is larger than a lasing beam diameter.

Trace NO 2 detection based on differential cavity ringdown spectroscopy using a dual wavelength passively locked external cavity diode laser

We successfully demonstrated NO2 detection based on differential absorption cavity ringdown spectroscopy using a dual wavelength passively locked external cavity diode laser. Selective trace NO2 detection was achieved in a 2 ml compact ringdown cell.

Novel NO/sub 2/ detection based on cavity ringdown spectroscopy using a power build-up cavity

This paper reports a laser diode pumped power build-up cavity (PBC) to apply for cavity ringdown spectroscopy (CRDS). The PBC is a compact-high finesse external cavity laser diode, which can obtain resonant enhancement without active cavity length control. PBC is applied generally undesired feed backed beam to cavity resonant enhancement. More than 2.30 /spl mu/s of ringdown time was achieved with a very small gas sampling volume about 2.5ml. Sensitivity of 3.62 /spl times/ 10/sup -7/ cm/sup -1/ corresponding to NO/sub 2/ detection limit of less than 1.7 ppm was achieved.

Compact diode laser trace gas system with an optical fiber coupled flexible high-finesse external cavity based on cavity ringdown spectroscopy

A fiber coupled high-finesse external cavity diode laser for cavity ringdown spectroscopy was successfully demonstrated. The sensitivity of 1 times 10^-7 cm^-1 was achieved in a 1 cm³ remotely located ringdown cavity as a sensor head.